Distcc Cross-Compiling

IntroductionDisclaimer: This guide will appear vague and incomplete if you aren't sure what you're doing. This is intentional. This is specifically not designed for users new to software compilation and toolchain components.

This is the official cross-compiling method used at Arch Linux ARM. If you plan on building a lot of packages and want to speed up the process, the following guide will turn an x86 Linux computer into an ARM cross-compiler. It's also much easier than most cross-compile setups.

This guide makes use of distcc in order to not have to build a full ARM development environment on x86. As the distcc project website states, "distcc does not require all machines to share a filesystem, have synchronized clocks, or to have the same libraries or header files installed." This is particularly advantageous to us since all that is needed is a working cross-compiler for ARM on a faster machine, while controlling the build from an ARM computer that has all of the current libraries and headers.

Distcc
Before beginning, a distcc environment needs to be set up. Follow the Distributed Compiling with distcc guide to establish a master device. The x86 machines will be known as the clients.

Pre-built crosstool-ng toolchains
In lieu of building the toolchain as detailed below, if you are running a 64-bit Linux installation you can try to use these packaged toolchains that are employed in the official build system.

It is highly recommended to use these tarballs as they have been thoroughly tested, and are maintained to be version-matched to the current toolchain components for our ARM architectures.

If you want to save yourself time and configuration, see WarheadsSE's distccd-alarm package. This will generate 3 packages (one for each architecture), and contains configuration and systemd service units for each. It is for x86_64 only, like these toolchain tarballs.

Install crosstool-ng
This process is very automated, courtesy of crosstool-ng. As a normal user (not root!), download the latest version (1.19.0 as of this revision) to a directory called "cross" in your home directory and extract it. Enter the source directory and configure with a prefix for the "cross" directory, make, and make install. If you are missing any pre-requisites, the configure script will let you know what they are.mkdir -p cross/src
cd cross
wget http://crosstool-ng.org/download/crosstool-ng/crosstool-ng-1.20.0.tar.bz2
tar -xjf crosstool-ng-1.20.0.tar.bz2
cd crosstool-ng-1.20.0/
./configure --prefix=/home/your_user/cross
make
make install

At this point crosstool-ng is ready to be configured. The program "ct-ng" in the "bin" directory is where the magic happens. It also has a menu configuration like the Linux kernel.

Downloading a CrossTool Configuration
Download the default .config file to place in "~/cross/bin" as shown below. Once you do this, do not run "menuconfig" or values will be overwritten. Choose either v5, v6, or v7 depending on the target platform.

Make nice with distcc
The toolchain will install under "~/x-tools" for armv5, "~/x-tools6h" for armv6 hard-float, and "~/x-tools7h" for armv7 hard-float. You can move this somewhere else if you like, or leave it where it is. Before we can use the compiler binaries that were created, links need to be created to make their names more appropriate. When compile jobs are sent to distcc, the program specified in the CC environment variable on the build master is what gets executed on the build clients. All the binaries that have been produced by crosstool-ng are in the correct format specifying the target platform as a prefix, though not with the correct platform and lacking tuple-less variants. This script will fix our problem. Make "~/x-tools[6h|7h]/arm-unknown-linux-gnueabi[hf]/bin/" writable and in there create a file called "link" and paste the following into it. Uncomment for your target architecture and run it.

Now the "bin" directory contains links with names that distcc will play nice with. To get distcc to use these binaries instead of the default system ones, we need to place this directory into the path for the distcc daemon:

Debian/Ubuntu: Edit "/etc/init.d/distcc"

Arch Linux: Edit "/etc/conf.d/distccd"

After the initial header block, add this line or modify PATH if it already exists in the file. Note that we are placing our binary directory at the very front. After making the change, restart the distccd daemon.PATH=/home/your_user/x-tools[6h|7h]/arm-unknown-linux-gnueabi[hf]/bin:$PATH

Compile!
Back on ARM "master" device, make sure that distcc has been enabled in makepkg.conf per the distcc guide, and specify the cross-compiler computer's IP address in the DISTCC_HOSTS variable. Now all builds using makepkg will make use of the distcc and cross compiler setup.

Crap, it's not working
If you've followed this guide to the letter and you know you've done everything right, the likely problem is that the user distccd is running as does not have permission to access the location of the crosstool-ng binaries. Either change distccd's user or relocate the x-tools directory to somewhere it can read it, then be sure the PATH set above reflects the new location.